"On many levels, Tumblr and Yahoo couldn't be more different, but, at the same time, they couldn't be more complementary.

"Yahoo is the internet's original media network.

"Tumblr is the internet's fastest-growing media frenzy."

Mr Karp, in a statement to "the Tumblr community", said the team was not changing.

"Our roadmap isn't changing," he said.

"And our mission - to empower creators to make their best work and get it in front of the audience they deserve - certainly isn't changing.

"But we're elated to have the support of Yahoo and their team who share our dream to make the internet the ultimate creative canvas."

The deal is expected to close in the second half of the year.

Analyst questions wisdom of Yahoo's purchase

Yahoo has been looking at a range of possible acquisitions since Ms Mayer took the helm last year and vowed to revive the company, which has faded in the face of competition from Google.

Tumblr could be key to Yahoo's strategy because of its popularity with younger internet users. A survey this year conducted by the online data group Survata found Tumblr more popular than Facebook among those aged 13 to 25.

While Tumblr generates very little cash, bringing it in the Yahoo family could offer the potential for new advertising and other revenue sources.

Roger Kay at Endpoint Technologies said the deal "brings a social element that Yahoo is missing and a set of new users".

But Mr Kay added that "paying $1.1 billion for a company with $13 million in revenue seems a little nuts to me".

"Those numbers aren't even earnings, which are surely negative," he said.

"So, even if Tumblr survives intact, Yahoo is unlikely to get its $1.1 billion back over any interval that falls within a human lifetime."

Founded in 2007 and headquartered in New York, Tumblr says it has more than 108 million blogs, 50 billion postings in 12 languages and 175 employees.

The website ranking site Alexa lists Tumblr as number 32 in terms of global popularity.